The degree of attention (interest) of a user to (in) display information displayed on a screen of a display apparatus is sometimes checked using a heat map.
It is considered that the degree of attention of a user to display information and the line-of-sight position in the screen have a close relationship to each other, and it has been proposed to create a heat map in which a gaze time period is represented by a change in color for each line-of-sight position (for example, refer to International Publication Pamphlet Nos. WO 2011/074198, WO 2012/105196, WO 2015/064080, and WO 2016/052646). Since this visualizes a corresponding relationship between display information displayed on the screen of the display apparatus and the gaze time period, information gazed for a long period of time and information gazed for a short period of time by the user may be identified from each other.